• Title/Summary/Keyword: 박리영역

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Characteristics of Fluid Force Reduction for Two Different Square Prisms in a Tandem Arrangement (직렬배열에 놓인 크기가 다른 정방형주의 유체력 저감특성)

  • Ro, Ki Deok;Kang, Chang Whan;Park, Kwon Ho
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.41 no.7
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    • pp.435-443
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    • 2017
  • The Characteristics of the flowfields of a square prism having a small square prism were investigated by measuring of lift and drag on the square prism and visualizing the flowfield using PIV. The experimental parameters were the width ratios(H/B=0.2~0.6) of small square prisms to the prism width and the gap ratios (G/B=0~3) between the prism and the small square prism. The drag reduction rate of the square prism initially increased and then decreased with the G/B ratio for the same H/B ratio, and increased with the H/B ratio for the same G/B ratio. The maximum drag reduction rate of 98.0% was observed at H/B=0.6 and G/B=1.0. The lift reduction rate of the square prism was not affected by the width and gap ratios; the total average value was approximately 66.5%. In case of a square prism having a small square prism, the stagnation regions were represented in the upstream and downstream sides of the square prism.

Petrological and mineralogical characteristics of the rocks constituting the Sungryemun (South Gate) (숭례문 구성 석재의 암석학적 및 광물학적 특징)

  • 박찬수;이상헌
    • The Journal of the Petrological Society of Korea
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    • v.12 no.4
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    • pp.196-206
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    • 2003
  • The geochemical and mineralogical investigation on the rocks and repair material comprising of the Sungryemun (The 1st National Treasure) has been made. Rock of the Sungryemun is highly weathered coarse-grained calc-alkali granite. The rock consists mainly of quartz, perthite, plagioclase and biotite with small amounts of orthoclase, muscovite, chlorite and sericite, which are major weathering products from perthite. For obtaining informations about degree of weathering, mineral composition of the original rock calculated by CIPW norm and weathered rock composition determined by XRD quantitative analysis were plotted on a ternary diagram of quartz-potash feldspar-plagioclase. Original rock compositions are plotted on the central granite area. whereas weathered ones are plotted on the granite area close to quartz. The result means that quartz is more abundant in weathered rock, due to selective chemical weathering of potash feldspar and plagioclase over quartz. On the whole, surface of the rocks were black-coated, exfoliated and highly fractured due to the physical and chemical weathering and heavy load has made the cracks in the lower parts of the stone construction. Also, cement and nails, which was used as repair material, during the repair work in the early 1960's, has accelerated the weathering process. Furthermore, weathered conditions of repair materials are very severe. Therefore, it is very urgent to establish of the conservation plan for the Sungryemun.

Evaluation of Slope Stability and Deterioration Degree for Bangudae Petroglyphs in Ulsan, Korea (울산 반구대암각화의 손상도 및 사면안정성 평가)

  • Lee, Chan-Hee;Chun, Yu-Gun;Jo, Young-Hoon;Suh, Man-Cheol
    • Journal of Conservation Science
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    • v.28 no.2
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    • pp.153-164
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    • 2012
  • The major petroglyphs of Bangudae site were composed mainly of hornfelsed shale. Surface of the rock was formed weathering layer (average porosity 25%) that discriminated mineral and chemical composition against fresh rock (average porosity 0.4%). The lost area of major petroglyphs in the past up images carved to the present was calculated about 23.8%. And occurrence area of exfoliation indicated 1.2% of the whole petroglyphs. As a result of the chromaticity analysis, color of the major petroglyphs was changed brighter and yellower than fresh rock by chemical and biological weathering factors. Average ultrasonic velocity of petroglyphs was measured 2,865m/s. This result indicated that ultrasonic velocity decreased especially bottom of petroglyphs than measured result in 2003 year. The results of the evaluation for slope stability, it identified the possibility of toppling, planar and wedge failure in host rock. The 3D image analysis and modeling data of the cavern obtained for structural reinforcement.

Evaluation and Weathering Depth Modeling of Thermally Altered Pelitic Rocks based on Chemical Weathering and Variations: Ulju Cheonjeon-ri Petroglyph (화학적 풍화작용과 조성변화에 따른 열변질 이질암의 풍화심도 모델링 및 평가: 울주 천전리 각석)

  • LEE Chan Hee;CHUN Yu Gun
    • Korean Journal of Heritage: History & Science
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    • v.56 no.4
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    • pp.160-189
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    • 2023
  • The Cheonjeon-ri petroglyph is inscribed with shale formation belonging to the Daegu Formation of the Gyeongsang Supergroup in the Cretaceous of the Mesozoic Era. This rock undergoes thermal alteration to become hornfels, and has a high hardness and dense texture. Rock-forming minerals have almost the same composition as quartz, alkali felspar, plagioclase, calcite, mica, chlorite and opaque minerals, but calcite is rarely detected in the weathered zone. The petroglyph forms a weathered zone with a certain depth, and there is a difference in mineral and chemical composition between weathered and unweathered zones, respectively. The CaO contents of the weathered zone were reduced by more than 90% compared to that of the unweathered zone, because calcite reacted with water and dissolved. As a result of calculating the surface weathering depth for the petroglyph with the transmission characteristics of X-rays, depth of the parts in falling off and exfoliation showed a depth of about 0.5 to 1 mm, but the weathering depth in most areas was calculated to be about 3 to 4 mm. This can be proved by the contents and changes of Ca and Sr. The surface discolorations of the petroglyph are distributed with different color density, and the yellowish brown discoloration is alternated with a thin biofilm layer, showing a coverage of 79.6%. Therefore, periodic preservation managements and preventive conservation monitoring that can effectively control the physicochemical and biological damages of the Cheonjeonri petroglyph will be necessary.

Change of Regional Myocardial Blood Flow After Transmyocardial Laser Revascularization in Porcine Model of Chronic Myocardial Ischemia (돼지 만성 심근허혈 모델에서 경심근레이저혈류재건술 후 국소 심근 혈류량의 변화)

  • Park, Kay-Hyun;Ahn, Hyuk
    • Journal of Chest Surgery
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    • v.34 no.9
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    • pp.662-671
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    • 2001
  • Background: This study was aimed to assess improvement in myocardial perfusion after TMR by measuring regional myocardial blood flow(RMBF) in porcine model of chronic myocardial ischemia. Material and Method: Ameroid ring was placed around the proximal left circumflex coronary artery in fourteen pigs. After 4 weeks, the control group(7 pigs) underwent rethoracotomy only, and the TMR group(7 pigs) underwent Ho:YAG laser TMR at the circumflex territory. After another 4 weeks, the animals were sacrificed for the measurement of RMBF using colored microspheres. The ratio of RMBF between the circumflex territory and the interventricular septum was calculated and compared. Result: At 4 weeks after ameroid constriction, RMBF of the circumflex territory decreased to 46∼89% of RMBF of the interventricular septum. In five of six animals in the TMR group, RMBF of the circumflex territory at 8 weeks after ameroid constriction was higher compared with RMBF at 4 weeks after ameroid constriction. However, the improvement was statistically significant only in two animals. In three of the four animals in the control group, RMBF of the circumflex territory also increased at 8 weeks compared with RMBF at 4 weeks. The degree of increase in RMBF was not different between the control and the TMR groups. Conclusion: In porcine model of chronic myocardial ischemia, the degree of increase in RMBF of the ischemic area after Ho:YAG TMR was not different from the increase by development of native collateral circulation. Perfusion of ischemic myocardium after TMR is not thought to improve to the degree that can be demonstrated by currently available method of assessment such as radioisotope myocardial scintigraphy.

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Exhaust Plume Behavior Study of MMH-NTO Bipropellant Thruster (MMH-NTO 이원추진제 추력기의 배기가스 거동 해석 연구)

  • Kim, Hyeonah;Lee, Kyun Ho
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.45 no.4
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    • pp.300-309
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    • 2017
  • A spacecraft obtains a reaction momentum required for an orbit correction and an attitude control by exhausting a combustion gas through a small thruster in space. If the exhaust plume collides with spacecraft surfaces, it is very important to predict the exhaust plume behavior of the thruster when designing a satellite, because a generated disturbance force/torque, a heat load and a surface contamination can yield a life shortening and a reduction of the spacecraft function. The purpose of the present study is to ensure the core technology required for the spacecraft design by analyzing numerically the exhaust gas behavior of the 10 N class bipropellant thruster for an attitude control of the spacecraft. To do this, calculation results of chemical equilibrium reaction between a MMH for fuel and a NTO for oxidizer, and continuum region of the nozzle inside are implemented as inlet conditions of the DSMC method for the exhaust plume analysis. From these results, it is possible to predict a nonequilibrium expansion such as a species separation and a backflow in the vicinity of the bipropellant thruster nozzle.

Fretting Wear Test of Inconel 690 Tubes Employing Piezoelectric Actuator (압전 구동기를 이용한 인코넬 690 튜브의 프레팅 마멸시험)

  • Chung, Il-Sup;Lee, Myung-Ho;Park, Ki-Hong;Lee, Jung-Hoon;Kwon, Jae-Do
    • Journal of the Korean Society for Precision Engineering
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    • v.26 no.2
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    • pp.101-108
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    • 2009
  • A fretting wear test rig for dry ambient condition, which employs a piezoelectric actuator, has been developed. It is driven and loaded in a very simple manner with acceptable experimental accuracy. By using the rig, Inconel 690 tube has been tested under the normal load of 10 and 15N with sliding amplitude of less than $100{\mu}m$ during $10^6$cycles. The wear resistance of the material has been characterized in terms of the wear coefficient based on the work rate model. SEM micrographs show the complex structures of the scars, which consist of risen peaks, plate-type thin layers and locally exposed bare surfaces. The cracks spread over the layers give clue to the fretting wear mechanism of the material.

Clinical Evaluation of Video-Assisted Thoracic Surgery (VATS) (비디오 흉강경 수술의 임상적 고찰)

  • 원경준;최덕영
    • Journal of Chest Surgery
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    • v.29 no.10
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    • pp.1133-1137
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    • 1996
  • From September 1994 to October 1995, we are reporting clinical results of 67 patients whom underwent video-assisted trio rabic surgery(VATS). 1. They were diagnosed as spontaneous pneumothorax In )5, diffuse interstitial lung disease in 9, empyema in 7, hemothorax in 5, malignant pleural effusion in 3, hyperhidrosis in 3, foreign body in chest cavity in 2, mesothelioma in 1, miliary tuberculosis in 1 and organizing pneumonia in 12. In pneumothorax, bullectomy in 33 and open bellectoiny in 2 due to pleural adhesion was done Hemostasis in 5, irrigation in 7, foreign body removal in 2, talcum powder insufrlation in 3, sympathectomy 3 as done. Thoracoscopic biopsy watt done In 12 3. For pneumothorax, operation was indicated as recurrent pneumothorax in 18, persistent air leak in 12, visible bullae In chest X-ray in 5. 4 Thoracoscopic biopsy was done in 12. They were interstitial pulmonary fibrosis in 9, miliary tuberculosis in 1, mesothelioma in 1, and organizing pneumonia in 1 .Among interstitial pulmonary fibrosis, usual interstitial pneumonia were 2 and diffuse interstitial pneumonia were 7. 5. Wo complication was found in 6) patients among 67 patients. The complication was found in 4 patients (2 persistent air leak, 2 contralateral lung atelectasis). We concluded that VATS was safe and beneficial in reducing postoperative complication and the role of thoracic surgery will increase markefdly.

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Characteristics of Flowfield of a Circular Cylinder Having a Detached Splitter Plate with High Reynolds Number (고 레이놀즈 수에서 분리된 분할판을 가진 원주의 유동장 특성)

  • Ro, Ki Deok;Lee, Han Gyun;Lee, Jong Ho;Lee, Jeong Min;Shin, Jin Ho;Cheon, Kang Bin
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.40 no.6
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    • pp.373-381
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    • 2016
  • In this study, we investigate the characteristics of the drag reduction of a circular cylinder having a detached splitter plate at the wake side. We measure the fluid force on a circular cylinder and visualize the field using particle image velocimetry (PIV) with a high Reynolds number, Re = 10,000. The experimental paraeters used were the width ratios (H/B = 0.5~1.5) of splitters to the prism width and the gap ratios (G/B = 0~2) between the prism and the splitter plate. The drag-reduction rate of the circular cylinder increased with H/B in the case of the same G/B, and it increased and then decreased with G/B in the case of the same H/B. The vortices of the opposite direction on the upper and lower sides of the detached splitter plate were generated by installing the plate. Reverse flow was caused by the vortices at the wake region of the circular cylinder, and the drag of the circular cylinder was decreased by the reverse flow.

Numerical Study on the Arrangement of AIG for Determining the $NH_3$ Concentration Distribution in the Package Type of Small Scale SCR System (패키지형 소형 SCR 시스템 내 $NH_3$ 농도분포 제어를 위한 AIG의 배치에 관한 전산해석적 연구)

  • Park, Seon-Mi;Chang, Hyuk-Sang;Zhao, Tong
    • Journal of Korean Society of Environmental Engineers
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    • v.33 no.5
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    • pp.368-377
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    • 2011
  • A package type of SCR (selective catalytic reduction) system that was proposed for removing the $NO_x$ found in flue gas from the small scale of air pollution sources was evaluated. The efficiency of the SCR system is determined by the proper utilization of catalytic media installed inside of the system, and the proper distribution of flow velocity and $NH_3$ concentration in the flue gas is a crucial factor for using the catalytic media. In this study, the distributions of $NH_3$ concentration were estimated under the various arrays and shapes of AIG at the given gas flow condition. The value of RMS (%) in $NH_3$ concentration is 95.3% at co-current flow (at $0^{\circ}$) injection but it is 90.1% at the condition of counter-current flow (at $120^{\circ}$) condition, which implies the counter-current injection is more favorable. By rearranging the $NH_3$ injection flow rates based on the distribution of velocity and $NH_3$ distribution in basic calculation, the value of RMS (%) in $NH_3$ concentration was reduced to 62.8%. The enhanced effect of $NH_3$ mixing by the combined effect of arrays and shapes are complied in the study.